1. Field of the Invention
The invention relates to an improved and simplified method for determining and correcting the angular offset of two shafts of machines or machine components which due to their parallel offset are connected to one another by way of two universal joints and a third shaft which connects the two universal joints.
2. Description of Related Art
It is conventional to equalize offsets between two shafts which connect engines and driven assemblies to one another via two universal joints and a third shaft. But this arrangement can only equalize parallel offsets. When the two shafts are not aligned exactly parallel to one another, serious damage often occurs due to an angular offset.
The two types of offsets, specifically parallel offset and angular offset, can be easily and accurately determined with optoelectronic alignment devices. However, this is only possible in the simpler case when the two shafts which are connected to one another run coaxially. These optical alignment devices based on lasers or other light sources and photosensitive detectors (PSD, CCD arrays or CMOS arrays) are described in German Patent DE 39 11 307 (which corresponds to U.S. Pat. No. 5,026,998) and German Patent DE 33 20 163 (which corresponds to U.S. Pat. No. 4,698,491). In these documents, alignment devices are described which, on the one hand, contain a light source in a measurement head and a detector in a second measurement head. In the measurement head, both the incidence position and also the incidence direction of a light beam can be measured by there being two detectors in succession in the beam path of the measurement head which can be read out two-dimensionally. This arrangement can be achieved, for example, via a beam splitter. On the other hand, measurement devices are also described in which one measurement head contains both a light source and also a two-dimensional detector, while the second measurement head contains a reflector, for example, in the form of a ridge prism. The alignment devices which are described in the aforementioned documents use light beams of point cross section and detectors which can be read out two-dimensionally.
German Patent Application DE 10 2006 023 926 (which corresponds to U.S. Pat. No. 7,672,001) describes alignment devices in which light beams are fanned out transversely relative to the propagation direction in more than one direction. Some embodiments call for each measurement head to contain both a light source and also a detector. The aforementioned optical alignment devices assume that the points of impact of the light beam or light beams on the detector or detectors is measured in several (at least three, but usually four or even five or more) rotary positions of the two shafts.
German Patent DE 33 35 336 (which corresponds to U.S. Pat. No. 4,518,855) describes an alignment device in which each measurement head contains both a light source and also detectors which can be read out two-dimensionally according to the site of incidence and angle of incidence. This measurement device is able to determine a misalignment according to angular and parallel offset in only one rotary position of the two shafts from one measurement of the points of impact on the detectors when the orientation of this rotary position and the points of impact are known for well aligned shafts by a comparison measurement on a single straight shaft. Measurements on the shafts which are to be aligned in different angular positions are, however, also fundamentally possible.
Often, special matching devices are employed for the use of these optoelectronic alignment devices for shafts which do not run coaxially, which therefore have a parallel offset and are connected via two universal joints and a third shaft. This device is shown in European Patent EP 1 430 995 (which corresponds to U.S. Pat. No. 7,242,465). The disadvantage in the use of these devices is that often the third shaft must be removed. Moreover, complicated handling of the devices and execution of a host of steps is necessary, which makes determining an angular offset complex and fault-susceptible. Thus, it can happen that an already correctly aligned machine is unintentionally shifted when the third shaft is re-installed. Another problem is that these devices are produced with overly large tolerances so that measurement of the angular offset becomes too inexact due to play.